Digital buffer characteristics: For a device used purely as a buffer/driver between logic stages, which input/output impedance combination is most desirable to avoid loading the source while strongly driving the next stage?

Introduction / Context:
Digital buffers isolate a signal source from a load, preventing excessive loading of the previous stage and providing adequate drive to the next stage or external circuitry. Impedance characteristics determine how well the buffer performs this role.

Given Data / Assumptions:

• Buffer operates in a rail-to-rail digital environment.
• Focus is on DC/low-frequency loading, not transmission-line matching.
• Goal: maximize signal integrity and fanout.

Concept / Approach:
A high input impedance minimizes current drawn from the source, reducing voltage droop and preserving logic levels. A low output impedance allows the buffer to source/sink current to quickly charge/discharge input capacitances of multiple loads, keeping VOH/VOL within spec. This combination provides isolation and strong drive.

Step-by-Step Solution:
Identify buffer role: isolate and drive.Select high input impedance to avoid loading the previous stage.Select low output impedance to drive the next stage with fast edges and adequate margins.Therefore, the best choice is high input impedance and low output impedance.

Verification / Alternative check:
Datasheets for dedicated line drivers and logic buffers specify tiny input currents and strong IOH/IOL with low VOL and high VOH at rated loads.

Why Other Options Are Wrong:
High output impedance cannot drive loads effectively.

Low input impedance unnecessarily loads the source.

“Matched impedances” applies to transmission lines, not generic logic buffering.

Common Pitfalls:
Overlooking capacitive loading and edge-rate control; in high-speed designs, series damping resistors may still be required despite low output impedance.

Final Answer:
high input impedance and low output impedance